JPH0339926Y2 - - Google Patents

Description

[Detailed description of the invention] [Technical field] The invention is a frequency modulation crystal oscillation circuit, more specifically, a frequency modulation crystal oscillation circuit, more specifically, a frequency modulation crystal oscillation circuit, in which a modulation voltage is applied to an oscillation section equipped with a crystal oscillator and a varicap connected in series with the crystal oscillator. The present invention relates to a frequency modulation crystal oscillation circuit that includes a modulation section that controls the output frequency of the oscillation section.

[Background Art] Generally, this type of frequency modulation crystal oscillator circuit, as shown in FIG. and a modulation section M that applies voltage to shift the output frequency of the oscillation section O. Incidentally, the output frequency of the oscillation section O varies depending on the ambient temperature due to the temperature characteristics of the crystal resonator X and the temperature characteristics of the oscillation transistor _Q1 of the oscillation section O, and it is necessary to correct this. However, when no modulation is being performed, the output of the voltage dividing section D constituted by the first resistor _R1 and the second resistor _R2 is applied as the modulating voltage to the variable cap V, and the input signal to the modulating section M is applied to a predetermined value. When the voltage is above the level, the modulating transistor _Q2 is turned on, and the output voltage of the voltage dividing section D is determined by the voltage dividing ratio of the parallel resistance of the emitter resistor R _E and the second resistor _R2 and the first resistor _R1 . is determined, it is necessary to perform temperature correction separately for non-modulation and modulation.

[Purpose of the invention] The invention was developed in view of the above points, and its main purpose is to ensure that the output frequency changes even when the ambient temperature changes, regardless of whether it is modulated or not modulated. The purpose of the present invention is to provide a frequency modulation crystal oscillator circuit that does not require frequency modulation.

[Disclosure of the invention] (Examples) Examples of the invention will be described below based on the drawings. As shown in FIG. 1, it is composed of an oscillation section O equipped with a crystal oscillator X, and a modulation section M that applies a modulation voltage to a variable cap V connected in series with the crystal oscillator X. The oscillator O is a normal non-modulated oscillator circuit in which one end of a crystal resonator X is connected to the base of an oscillating transistor _Q1 , and the other end of the crystal resonator X is connected to one end of a varicap V. The modulation section M includes a modulation transistor _Q2 , a voltage dividing section D in which a first thermistor _T1 and a resistor R are connected in series and inserted between both ends of a power supply with the first thermistor _T1 on the high voltage side, and a voltage dividing section D for modulation. A second thermistor _T2 is connected as an emitter resistance of the transistor _Q2 , and the modulation voltage to the variable cap V is applied as the output voltage of the voltage dividing section D. The input to the modulation section M is input to the base of the modulation transistor _Q2 . The modulation transistor _Q2 acts as a switching element, and is turned off when there is no input signal, and turned on when the input signal exceeds a predetermined level. However, when there is no signal, that is, when there is no modulation, a modulation voltage determined by the voltage division ratio between the first thermistor _T1 and the resistor R is applied to the variable cap V, and during modulation, the voltage is applied to the second thermistor via the modulation transistor _Q2 . _T2
and a resistor R are connected in parallel, and this parallel resistor and the first resistor R are connected in parallel.
A modulation voltage determined by the voltage division ratio between the thermistor _T1 and the thermistor T1 is applied to the variable cap V. In this way, when there is no modulation, the first thermistor _T1 adjusts the modulation voltage in accordance with the ambient temperature, while when modulation, the first thermistor _T1 and the second thermistor _T2 The modulation voltage is corrected by , and the output frequency of the oscillator O becomes stable regardless of whether it is modulated or not modulated.

[Effects of the invention] As described above, the modulation section of the invention includes a switching element that is turned on when the input signal is above a predetermined level and turned off when there is no input signal, and a resistance that changes depending on the ambient temperature. A first temperature-sensitive resistor whose value changes is connected in series with a resistor, and when the switching element is in the OFF state, a modulation voltage is applied to the varicap so as to keep the output frequency of the oscillator constant in response to changes in ambient temperature. A voltage dividing section to be controlled and a temperature sensitive resistor whose resistance value changes depending on the ambient temperature, which is connected in parallel to one of the resistors constituting the voltage dividing section via the switching element, and the switching element is in an on state. The device is equipped with a second temperature sensing element that controls the modulation voltage to the variable cap so as to keep the output frequency of the oscillator constant in response to changes in ambient temperature. The modulation voltage to the varicap is adjusted by the resistor, and when there is no modulation, the modulation voltage to the varicap is adjusted by at least the second temperature-sensitive resistor.
This has the advantage that the output frequency can be stabilized without changing even if the ambient temperature changes even when no modulation is performed.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing one embodiment of the present invention;
The figure is a circuit diagram showing a conventional example. D is the voltage dividing section, M is the modulation section, O is the oscillation section, _Q2 is the modulation transistor, R is the resistor, _T1 is the first temperature sensitive resistor, _T2 is the second temperature sensitive resistor, and V is the varicap. , X is a crystal oscillator.

Claims (1)

[Scope of utility model registration request] It consists of an oscillation section equipped with a crystal resonator, and a modulation section that controls the output frequency of the oscillation section by applying a modulation voltage to a varicap connected in series with the crystal resonator. A switching element that is on when the input signal is on and off when there is no input signal, and a first temperature-sensitive resistor and a resistor whose resistance value changes depending on the ambient temperature are connected in series so that the switching element is off. A voltage dividing section controls the modulation voltage to the varicap so as to keep the output frequency of the oscillation section constant in response to changes in ambient temperature when A varicap is connected in parallel to one of the resistors constituting the voltage dividing section via the switching element, and is configured to keep the output frequency of the oscillation section constant in response to changes in ambient temperature when the switching element is in the on state. A frequency modulation crystal oscillation circuit comprising: a second temperature sensing element for controlling a modulation voltage to the frequency modulation crystal oscillation circuit;